The long-term goals of this research are (1) to evaluate radiation-induced changes at the cellular level in the immature nervous system; (2) to use ionizing radiation as a tool to study reparative and regenerative capacities of the immature nervous system; and (3) to study aspects of postnatal development of the spinal cord. The experiments take advantage of two unique models developed in this laboratory. One model involves induction of Schwann cell development in the central nervous system (CNS) by irradiating the lumbosacral region of the cord in 3-day-old rats. Schwann cells are the normal glia of the peripheral nervous system (PNS), where they play an important role in regenerative processes which proceed with much greater facility in the PNS than in the CNS. Specific Aim I will characterize the relationships established between intraspinal Schwann cells and the neurons and vasculature in the ventral spinal gray matter and will explore the possibility that alterations in astrocytes contribute to access of Schwann cells to the CNS. These relationships will be examined light and electron microscopically and immunohistochemically. Specific Aim II will examine conditions necessary for establishment of Schwann cells within the irradiated spinal cord by transplanting cultured Schwann cells into this environment. These Specific Aims provide unique opportunities to expand our knowledge of relationships between Schwann cells and the cellular constituents of the CNS, an understanding fundamental to attempts to use transplanted Schwann cells to effect repair in the CNS. The other model is a radiation-induced glial-depleted state existing at a time when the glial population is developing and maturing in the non-irradiated spinal cord. Earlier in vivo studies showed that, depending upon the amount of radiation administered, myelin formation by oligodendrocytes could be delayed in either a short-term or a protracted fashion. In Specific Aim III glial cell cultures will be established from spinal cords of rats exposed to these two levels of radiation. Immunocytochemical analysis of the cultures, as compared with those derived from non-irradiated spinal cords, will be performed in an attempt to determine if differing populations of glia are altered by these levels of radiation exposure. This correlative in vitro study may provide insights which could not be gained from earlier in vivo studies. Finally, Specific Aim IV will utilize the glial-depleted model as a background upon which to manipulate further the glial cell populations and to test their roles in preventing regeneration of axons in the CNS. Previous studies from this laboratory have demonstrated that axons will regenerate in the irradiated, glial-deficient spinal cord. In the proposed study, glial cultures will be transplanted into the irradiated spinal cord following a dorsal root lesion in an attempt to inhibit axonal regrowth into the spinal cord. Axonal tracing techniques will be combined with immunocytochemistry and ultrastructure to evaluate axonal-glial interrelations that may promote regeneration in this unique model.